A copper foil is generally used as a current collector of a medium and large lithium battery for a Hybrid Electric Vehicle (HEV). As the copper foil, a rolled copper foil by rolling processing is mainly used, but manufacturing cost of the rolled copper is high and it is difficult to fabricate a copper foil having a wide width.
Further, the rolled copper foil uses lubricating oil during the rolling processing, so that adhesion with an active material may be degraded by a contamination of the lubricating oil, so that a charging and discharging cycle characteristic of the battery may be degraded.
A lithium battery has a change in volume during charging and discharging and accompanies a heating phenomenon according to overcharging. Further, adhesion with an electrode active material needs to be improved. When a thickness of a current collector in the lithium battery is large, a capacity per volume of the lithium battery may be decreased. Accordingly, a highly elongated and highly strong copper foil, which is capable of resisting to a change in volume and a heating phenomenon of the lithium battery and has excellent adhesion with an active material, is required.
Accordingly, a copper foil having a small thickness, high mechanical strength, and a high elongation property is required.